A crop harvester is an extremely complicated and unwieldy piece of farm equipment. The operator of a typical standing-crop harvester must constantly survey various aspects of the harvesting operation, such as cutting height, obstacles in the path of the harvester, proper discharge of the cut crop to the wagon, and the like. It is absolutely essential that the harvesting machine be used with maximum efficiency, as the proper harvesting time must be observed and the elevated cost of the machinery requires its efficient use.
It has therefore been suggested as described in the above-copending application to provide automatic means for controlling the height of the harvesting implement on the front of the agricultural machine. It has also been suggested to provide automatic steering means which senses the edge of a cut swath and automatically guides the harvester along this edge so as to obtain a cut of maximum possible width without the driver's supervision. Thus the operator can merely guide the machine manually as he cuts his first swath and at each end of each swath; in between the machine automatically will guide itself and he can attend to other phases of the harvesting operation.
Relative to the normal direction of travel of the harvester the back wheels are usually the steered wheels, so as to permit the machine to turn in a minimum radius, literally making it possible for the machine to pivot on one of the front wheels. These rear wheels are usually operated by a double-acting hydraulic cylinder controlled from a power-steering arrangement at the driver's station. The automatic pilot is switched on by the driver and serves to operate this double-acting cylinder in accordance with an output produced by the crop sensor which is mounted on the front of the harvester. When the steering wheel is not in use the operator must throw the automatic steering control switch, and thereafter keep his hands free of the steering wheel which follows movements of the rear steered wheel. Since it is customary practice to provide such harvester steering wheels with a so-called spinner knob this continuously moving steering wheel presents a considerably hazard for the operator.
Another disadvantage with the known automatic steering systems is that the harvester is inadequately controlled when operating on a slope or inclination so that it tends to move in a downhill direction, the automatic steering controls frequently being inadequate to cope with this downhill bias. Furthermore, such a servosteering system frequently hunts excessively, as a result of the crop sensor only cancelling a steering instruction after an excessive steering compensation, so that the harvester is constantly hunting for a proper path.
Further disadvantages of such systems is that the steering composition which is necessary to correct the course at relatively low harvester speeds is excessive at high harvester speed so that the steering-control is only effective at a predetermined operation speed of the device. Such a limitation is disadvantageous in that it prevents the automatic steering control from being used when the vehicle is operating at a normally high or low speed.
An automatic steering system as described above must be manually switched on and manually switched off. This requires an extra motion by the driver in case a potentially dangerous situation arises, such as an obstacle suddenly appearing in the path of the harvester. He must first shut down the automatic steering control and then manually steer the harvester around the obstacle. The necessity of previously preforming these two functions creates a potentially harzardous situation in that the response time for taking over manual steering of the harvester is considerably increased.